I don't know if deworming her will help or not.
This is not the first hen you've had that has had reproductive problems is it? Do her symptoms not look similar to you?
As posted, Safeguard is given orally, so no, it's not put in the water or feed. Here's how to give oral medications...
A swollen abdomen is often due to reproductive disorders or possibly organ failure.
I'd work on hydration, get the calcium into her. See if she will eat for you.
Safeguard liquid goat dewormer or equine paste is dosed orally by weight.
To treat Roundworms Only - Safeguard dose is 0.23ml...